The present invention relates to a shape measuring apparatus and method for measuring, with ultrahigh precision, the shape, surface roughness, undulation flatness, etc. of a measured surface in, for example, semiconductor wafers and aspherical lenses.
Recently, for measurement of, for example, surface configuration of semiconductor wafers, free curved surface configuration and surface roughness of aspherical lenses and the like, it has become necessary to satisfy measurement accuracy requirements to the order of submicron to nanometer levels or less. Three-dimensional measuring devices and surface roughness measuring devices known in the art typically have a construction as shown in FIG. 15. That is, on a surface plate 101, on which an object-to-be measured 102 is placed, there are mounted moving members 104, 105, 106 which are respectively operative to move a probe 103 in X, Y and Z directions as shown, the probe 103 having a function to contact a measured surface 102a of the object 102 to carry out measurement of surface configuration of the object. The moving member 104 is of a gantry shape and is slidable in Y direction along rails 107, 107 laid in parallel on the surface plate 101. The moving member 105, as X moving member, is mounted on a beam portion 104a of the moving member 104 and is slidable along the beam portion 104a in X direction. The moving member 106, as Z moving member, is so mounted to the X moving member 105 as to be slidable in Z direction and has a probe 103 at its lower end.
In such three dimensional measuring devices and the surface roughness measuring devices of the prior art, rollers, air slide, oil bearings, etc. are used as means for sliding respective moving members 104, 105, 106 in X, Y and Z directions. Where such means are used, however, there is a problem that when the moving members are moved several millimeters to several hundred millimeters, achievable moving straightness deviation is limited to about 1 .mu.m in one of the axial directions X, Y, Z. So, when the moving members are respectively moved in three axial directions X, Y, Z, the resulting moving straightness deviations, when totalled, would easily come up to the order of several micrometers. With the conventional measuring devices, therefore, it is impossible to measure the shape of such a measured surface as aforesaid to such a measurement accuracy of submicron meter to nanometer order or less. Similarly, aforesaid problem would occur with measuring devices of polar coordinate type and cylindrical coordinate type because the rotary table involves the problem of low accuracy in respect of moving circularity deviation.
As already stated, the conventional threedimensional measuring devices and the surface roughness measuring devices are of such arrangement that the probe 103 is moved and object 102 is not moved. However, no measuring device of reversed arrangement has been known such that the probe is held stationary and the object is moved.